Improving the effectiveness of defibrillation waveforms will allow the size of implantable cardioverter defibrillators to be reduced. Biphasic waveforms were a first step towards improving waveform effectiveness. However, for biphasic waveforms, the optimum strength of the second phase that minimizes the shock strength required for defibrillation is much larger than the optimum strength of the second phase that minimizes the amount of tissue damage caused by the defibrillation.
U.S. Pat. No. 4,637,397 to Jones and Jones, titled "Triphasic Wave Defibrillation", describes one effort to improve upon the biphasic waveform. This patent describes a method and apparatus for the stimulation of cells in arrhythmic myocardial tissues by administering, a triphasic waveform comprising, in sequence, a conditioning pulse, a defibrillating or correcting pulse of opposite polarity to the conditioning pulse, and then a healing pulse with the same polarity as the conditioning pulse. Jones does not suggest any particular implementation for their waveform. Rather, it is simply stated that means for applying the wave to fibrillating myocardial tissue "may comprise any convenient device conventionally used in practicing defibrillation techniques." (see Column 4 line 61 to Column 5 line 9 therein).
Unfortunately, the triphasic waveform suggested by Jones has not been successfully implemented. The problem is summarized in U.S. Pat. No. 5,522,853 to Kroll, which notes at column 2 lines 52-64 that: "the triphasic waveform suggested by Jones et al. has been shown to be no more effective than a traditional biphasic waveform. Manz, M. et al., Can Triphasic Shock Waveforms Improve ICD Therapy in Man? Supplement to Circulation, Vol. 88, No. 4, Part 2, Oct. 1993, Abst. 3193."